In copending U.S. patent application Ser. No. 051,367, filed 5/18/87 by Roland F. Gatturna et al. for "Suture Anchor", there is disclosed a variety of suture anchors of the sort adapted to anchor one end of a piece of conventional suture in bone, and there is disclosed several suture anchor installation tools for deploying such suture anchors in bone.
The specification and drawings of the above-identified U.S. patent application Ser. No. 051,367 is hereby incorporated by reference into the present patent application.
Looking now at FIG. 1, there is shown one of the suture anchors disclosed in the above-identified U.S. patent application Ser. No. 051,367. This suture anchor, identified generally by the numeral 105, comprises a coupling member 110 and a barb 115.
Coupling member 110 comprises a piece of 6A14V titanium alloy having a first end surface 120 and a second end surface 125. First end surface 120 is disposed at an angle of approximately 30 degrees to the coupling member's longitudinal axis, and second end surface 125 is disposed at a right angle to the coupling member's longitudinal axis, as shown. Coupling member 110 has a blind hole 130 opening on second end surface 125, and a bore 135 extending at an angle between the coupling member's side wall and its bottom end surface 120, as shown. Bore 135 extends at a right angle to the coupling member's bottom end surface 120. In the case of a suture anchor adapted to anchor a No. 0 suture (i.e., a suture having a diameter of approximately 0.014 inch), coupling member 110 preferably has a length of approximately 0.160 inch and a diameter of approximately 0.053 inch, blind hole 130 has a depth of approximately 0.070 inch and a diameter of approximately 0.028 inch, and bore 135 has a diameter of approximately 0.028 inch.
Barb 115 comprises a curved length of nickel titanium alloy having a first end 140 and a second end 145. In the case of a suture anchor adapted to anchor a No. 0 suture, barb 115 preferably has a diameter of approximately 0.026 inch and, in its unrestrained state, comprises an arc of approximately 135 degrees of a loop approximately 0.250 inch in diameter (when measured to the inside of the loop). Barb 115 is attached to the coupling member by fitting the barb's first end 140 into the coupling member's blind hole 130, whereby the barb's second end 145 extends upward and outward from the coupling member. Coupling member 110 is then crimped inward at one or more points as shown at 150 to lock barb 115 to the coupling member. Barb 115 is made of such a nickel titanium alloy that it is capable of being elastically deformed to a substantially straight length when desired (i.e., so that the barb's second end 145 is aligned with its first end 140, as well as with the opposite ends of the coupling member). By way of example, barb 115 may be made out of binary nitinol such as that sold by Furukawa of Japan and Raychem Corporation of Menlo Park, Calif., or it might be made out of ternary nitinol such as that sold by Raychem Corporation and described in U.S. Pat. No. 4,505,767 (Quinn).
Looking next at FIG. 2, there is shown one of the suture anchor installation tools disclosed in the above-identified U.S. patent application Ser. No. 051,367. This suture anchor installation tool, identified generally by the numeral 205, may be used to deploy the suture anchor shown in FIG. 1. Installation tool 205 comprises a hollow sheath or cannula 210, a hollow loader or inserter 215 and a solid (or hollow) plunger 220.
Hollow sheath 210 terminates in a flat annular surface 225 at its front end and a flat annular surface 230 at its rear end. Surfaces 225 and 230 are disposed at an angle substantially perpendicular to the longitudinal axis of sheath 210. Sheath 210 has an axial bore 235 extending between its front and rear surfaces 225 and 230. Sheath 210 includes a disk-like finger grip 240 which is affixed to the rear end of the outer sheath member and includes a flat surface 245 which is coplanar with the sheath member's rear surface 230. In the case of an installation tool adapted to deploy a suture anchor for anchoring a No. 0 suture, sheath 210 preferably has an outer diameter (i.e., forward of finger grip 240) of approximately 0.083 inch, an inner diameter of approximately 0.071 inch, and a length of approximately 4.0 inches.
Hollow loader 215 terminates in a flat annular surface 250 at its front end and a flat annular surface 255 at its rear end. Surfaces 250 and 255 are disposed at an angle substantially perpendicular to the longitudinal axis of loader 215. Loader 215 has an axial bore 260 extending between its front surface 250 and its rear surface 255. Loader 215 includes a disk-like finger grip 265 which is attached to the rear end of the loader member and includes a flat surface 270 that is coplanar with the loader's rear surface 255. Loader 215 is sized so that it will make a close sliding fit within bore 235 of sheath 210, as will hereinafter be described in further detail, and also so that its leading tip 250 will not protrude from the front end of sheath member 210 when the loader is inserted into the sheath's axial bore 235 and the loader's finger grip 265 is in engagement with the sheath's rear surface 230, as will hereinafter be described in further detail. In the case of an installation tool adapted to deploy a suture anchor for anchoring a No. 0 suture, loader 215 preferably has an outer diameter (i.e., forward of finger grip 265) of approximately 0.065 inch, an inner diameter of approximately 0.047 inch, and a length of approximately 4.13 inches.
Plunger 220 includes a solid (or hollow) body section 275 and a head section 280. Body section 275 has a round cross-section and terminates in a front surface 285. Plunger 220 is sized so that its body section 275 will make a close sliding fit within bore 260 of loader 215 and also so that its leading tip 285 will protrude from the front end of the loader member a short distance when the plunger's head section 280 is in engagement with the loader member's rear surface 270, as will hereinafter be described in further detail. In the case of an installation tool adapted to deploy a suture anchor for anchoring a No. 0 suture, plunger 220 preferably has a diameter of approximately 0.047 inch forward of head section 280, and a length of approximately 4.32 inches, as will hereinafter be described in further detail.
Installation tool 205 is intended to be utilized as follows. Looking next at FIG. 3, suture anchor 105 is loaded into the top end of sheath member 210 so that the suture anchor's coupling member 110 resides inside the sheath's axial bore 235 and the suture anchor's barb 115 extends above finger grip 240 of the sheath member. Looking next at FIG. 4, the front end 250 of loader 215 is then slipped over the free end of the suture anchor's barb 115 so that the free end of the barb extends into the loader member's axial bore 260. Then loader member 215 is (a) forced into coaxial alignment with outer sheath member 210, thereby straightening out barb 115 in the process, and (b) pushed into the interior of sheath member 210, carrying the suture anchor downward within the sheath member as it goes. In order to assure that barb 115 of suture anchor 105 is contained completely within loader 215 such that suture anchor loader surface 250 contacts suture anchor surface 125, the sheath's bottom surface 225 is rested against a stationary surface 305 (see FIG. 5) while suture anchor loader 215 is brought downward into direct contact with the suture anchor's rear surface 125. Sheath member 210 and loader member 215 are carefully sized relative to one another (and relative to suture anchor 105) so that when the loader member's finger grip 265 is thereafter brought into contact with the sheath member's top surface 245, the suture anchor will protrude slightly from the bottom end of the sheath member, as shown in FIG. 6. More specifically, as seen in FIGS. 7 and 8, sheath member 210 and loader member 215 are sized relative to one another (and relative to suture anchor 105) so that both ends of the suture anchor's diagonal bore 135 will be exposed to view when the loader member's finger grip 265 is brought into contact with the sheath member's top surface 245. With the suture anchor so held by the installation tool, a conventional suture 405 may then be easily attached to the suture anchor by passing the suture through the anchor's diagonal bore 135 and tying a knot 410 at the end of the suture which can then bear against the bottom end 120 of the suture anchor's coupling member, as shown in FIGS. 7 and 8.
Once the suture has been attached to the suture anchor in the foregoing manner, plunger member 220 may then be inserted into the loader member's internal bore 260 (see FIG. 9) and pressed downward until its bottom tip 285 contacts the suture anchor barb contained in the loader member's bore 260. By appropriately sizing the respective members involved, the head section 280 of the plunger member will remain slightly above finger grip 265 of loader member 215 when the plunger member's tip 285 engages barb 115 of suture anchor 105.
Thereafter, when the installation tool is actuated to deploy the suture anchor (and its attached suture) into bone, the tip of the installation tool is inserted into a hole 505 formed in a bone 510 until the suture anchor rests on the bone surface 515 (see FIG. 10), and then head section 280 of plunger member 220 is held stationary while finger grip 240 of sheath member 210 is pulled upward so that the loader's flat surface 270 engages the underside of the plunger's head section 280, thereby ejecting the suture anchor 105 (and its attached suture 405) out of the installation tool and into the bone, as shown in FIGS. 10 and 11.
Complete details regarding the construction and use of suture anchor 105 and installation tool 205 are provided in the above-identified U.S. patent application Ser. No. 051,367, which is incorporated herein by reference; the foregoing description is provided merely for convenient reference in understanding the present invention.
With the three-element installation tool 205 described above, a hole slightly larger in size than the combined diameters of the outer sheath member 210 and the suture 405 must be drilled in the bone. For example, with a suture anchor for anchoring a No. 0 suture, where the suture anchor's coupling member 110 has a diameter of approximately 0.053 inch, suture 405 has a diameter of approximately 0.014 inch, and outer sheath 210 has a diameter of approximately 0.083 inch, a hole approximately 0.098 inch in diameter must be drilled in the bone. In the case of a suture anchor for anchoring a No. 2 suture, where the suture anchor's coupling member 110 has a diameter of approximately 0.061 inch, suture 405 has a diameter of approximately 0.020 inch, and outer sheath 210 has a diameter of approximately 0.095 inch, a hole approximately 0.116 inch in diameter must be drilled in the bone.
A summary table of such sizing is given below:
TABLE 1 ______________________________________ Suture Size: No. 0 No. 2 ______________________________________ Suture Anchor Dia. 0.053 0.061 Sheath Diameter 0.083 0.095 Suture Diameter 0.014 0.020 -- -- Sheath + Suture Dia. 0.097 0.115 Drill Diameter 0.098 0.116 (Drill hole) - (Suture Anchor) 0.045 0.055 ______________________________________
Unfortunately, while the three-element installation tool 205 described above is known to work, it is also believed to suffer from a number of disadvantages.
For one thing, it will be seen from Table 1 above that the three-element installation tool 205 takes up a substantial amount of room in the bone hole relative to the diameter of the suture anchor. More specifically, as seen in Table 1 above, the suture anchor for anchoring a No. 0 suture has a coupling member diameter of approximately 0.053 inch, yet it requires a drilled hole of approximately 0.098 inch to accommodate the suture anchor when it is set by installation tool 205. Therefore, the suture anchor's barb must essentially take up the difference between the 0.053 inch coupling member and the 0.098 inch hole when the suture anchor is set in the hole. Thus, the barb must expand approximately 0.045 inch for the suture anchor used to anchor a No. 0 suture. Similarly, as seen in Table 1 above, the suture anchor for anchoring a No. 2 suture has a coupling member diameter of approximately 0.061 inch, yet it requires a drilled hole of approximately 0.116 inch to accommodate the suture anchor when it is set by installation tool 205. Therefore, the barb must essentially take up the difference between the 0.061 inch coupling member and the 0.116 inch hole when the suture anchor is set in the hole. Thus, the barb must expand approximately 0.055 inch for the suture anchor used to anchor a No. 2 suture. Inasmuch as the barb loses force as it returns closer and closer to its original curved shape from its constrained straight shape (e.g. much like a spring), the larger the difference existing between the bone hole diameter and the suture anchor body, the smaller the force applied to the side wall of the bone by the suture anchor's barb when the suture anchor is set in the bone, and hence the weaker the attachment of the suture anchor to the bone. Accordingly, a fit such as that mandated by the use of the three-element installation tool 205 could possibly lead to inconsistent anchoring of the suture in the bone.
Another disadvantage of the three-element installation tool 205 described above is that the outer sheath 210 and loader member 215 can be preloaded with the suture anchor (in the manner shown in FIGS. 5 and 6) but, if it is then left for a substantial amount of time between loading and use, the barb can lose its resiliency and relax over time, so that when the suture anchor is thereafter used, its barb may not contact the bone wall with the same force that it would have if the suture anchor had been used immediately after loading the suture anchor into sheath 210 and loader 215. Accordingly, preloading accompanied by delayed use can possibly lead to inconsistent and unsatisfactory anchoring of the bone anchor in the bone.